ABSTRACT COCHLEAR NONLINEARITY AND AUDITORY FUNCTION IN HUMANS This program of research includes studies that will: (1) provide insights into basic cochlear processes by describing the relationships among frequency, level and latency and between tuning and cochlear-amplifier gain, (2) evaluate the extent to which these insights improve our understanding of the consequences of cochlear damage, (3) determine whether behavioral response growth in subjects with both normal and impaired hearing can be predicted either from sensitivity loss or the relationship between acoustical and behavioral measurements of response growth, and (4) determine whether these relationships can be used to select individually customized signal-processing strategies that result in improved speech perception and/or are preferred by patients with hearing loss. This proposal is characterized by several new and innovative components. It will evaluate fundamental cochlear processes in humans using a newly described metric (gain-bandwidth product) to assess cochlear invariance with respect to gain and tuning, and it will describe changes in this new metric as a consequence of hearing loss. It also includes innovative translational research that will evaluate relationships between hearing loss, behavioral response growth, and DPOAE response growth, all of which have implications for the selection of signal-processing strategies to ameliorate the consequences of cochlear damage. Finally, studies performed as part of this program of research will go beyond describing the relationships between different estimates of response growth by determining which signal-processing strategy, selected on the bases of several different behavioral and acoustical measurements, improve speech perception and/or are preferred by patients with hearing loss. This translational research will have important implications for all patients with hearing loss, especially infants and young children who cannot describe their percepts of loudness.